1867.] Mining. 273 



best shown by transcribing the Doctor's somewhat unattractive 

 formula : 



" 18 HO + 5 Ca 0, CO a + 7 EO, Si 3 + 5 ^A, 

 SiO a + 3(MgO) 8 (Si0 8 ) a ." 



Until more shall be known as to the history of this complex 

 mineral, Dr. Emmerhng proposes to distinguish it as Pseudone- 

 pkriie. 



The eminent Eussian mineralogist, M. Kokscharow, has pub- 

 lished the results of his observations " On the Crystalline System 

 and the Angle of Sylvanite" (Ueber das Krystallsystem und die 

 Winkel des Sylvanits).* This mineral so rarely occurs crys- 

 tallized, that the system to which it belongs has always been 

 questionable, Mobs having described it as rhombic, while Gr. Eose 

 regarded it as oblique. Availing himself of some well-defined 

 crystals recently come into his possession, the author has under- 

 taken a complete investigation of the mineral, the results of which 

 confirm Eose's determinations as to the oblique character of the 

 crystals. 



In a paper " On certain Phenomena observed in Natrolite " 

 (Ueber einige Erscheinungen, beobachtet am Natrolith),f Professor 

 Kenngott describes the singular behaviour of this mineral in relation 

 to heat. When small colourless transparent crystals of natrolite 

 are slowly heated, they gradually become white and opaque, without 

 losing their crystalline form ; but if further heated, under proper 

 conditions, these altered crystals lose their colour and opacity, and 

 return to their original condition. The author explains these 

 appearances by supposing the mineral to be constituted according 

 to the following expression : — 



"NaO, 2H0 + A1 2 3 , 3 Si 2 ." 

 It will be observed that the soda, instead of being combined with a 

 portion of the silica, as usually represented, exists in the state of 

 a free hydrate, and the first effect of exposure to heat is to expel 

 the water from this hydrate, thus leaving the soda free, the 

 molecular change induced giving rise to the opacity ; but when the 

 altered mineral is further heated, the soda combines with the 

 silicate of alumina to form a clear fusible compound ; and hence 

 the crystals regain their transparency. The author perceived that 

 if this view of the constitution of natrolite be correct, the mineral 

 in its natural state should give an alkaline reaction, from the 

 presence of free hydrate of soda ; and this sagacious inference was 

 fully verified by his .experiments. When powdered natrolite is 

 moistened with distilled water, it gives a strong red tint to 

 turmeric paper, and restores the blue colour to reddened litmus. 



* ' Melanges Physiques et Ch uniques,' tome vi., liv. 5, p. 537. 

 t ' Neues Jahrbuch fur Mineralogie, u. s.w.,' 1867, Heft 1, p. 77. 

 VOL. IV. T 



